1. Field of the Invention
This invention relates to a method for finding the parameters in a functional relationship between the stimulation frequency in an implantable physiological stimulating device such as a heart pacemaker, and a sensor signal indicative of the physical load condition of a patient in whom the device is implanted.
2. Description of the Prior Art
Recently, pacemakers including a control system for matching the stimulation frequency of a heart pacemaker to the varying work load condition of a patient, generally referred to as rate responsive pacemakers, have been developed. Typically, rate responsive pacemakers rely on the sensing of a variable related to and indicative of the work load of a patient. Such variables are, for instance, blood oxygen saturation, blood pH, patient movement and force. The functional relationship between the sensed variable and the stimulation frequency could be linear or non-linear, depending on the sensed variable, the sensor type and the sensor signal processing.
Irrespective of the type of functional relationship, linear or non-linear as the case may be, the parameters in the function must be set to values which are optimal to the individual pacemaker patient, as the sensor output signals varies from patient to patient depending on general fitness, body constitution, pacemaker placement, etc.
In the prior art these technical parameters were directly set, as illustrated in an example of a prior art pacemaker disclosed in U.S. Pat. A-4,428,378. That known pacemaker has a sensor of the piezoelectric transducer type, and varies the stimulation frequency in response to sensed activity as a linear function with the slope as a programmable parameter. The slope parameter value is set by the physician and transmitted to the pacemaker by telemetry, to control pacemaker interaction with the patient.
However, directly setting the parameter values presents a problem to the physician because the mathematical character of these parameters, exemplified by slope in the type above, lack immediate or recognizable connection to the corresponding heart rate, which is the quantity familiar to the physician. Also, direct parameter value setting is inconvenient to the patient because an unexperienced physician must use a trial and error technique to find an optimal setting.